Not Junk: ‘Jumping Gene’ Is Critical For Early Embryo

Jumping genes, also known as transposons, are gaining momentum. They are considered either as slacking junks or maleficent parasites in our genome. As such, they are largely taken for granted. However, it seems the tables have turned. There seem to be certain jumping genes that without them we would not move past our embryonic state. Researchers from the University of California – San Francisco presented proof that certain jumping genes do perform a crucial role during the development of an embryo. Without them, the embryo would not progress as it should.1

Jumping genes — junk DNAs

Transposons are small segments of DNA with a special capability. They create copies of the genetic material and then insert at random sites in the genome.2 For that, they are dubbed as “jumping genes” based on the “jumping” activities that they do. Some consider jumping genes as junk DNA because they tend to replicate needlessly multiple copies of DNAs that already exist. Some of these genetic copies could be noncoding (junk) DNAs. Our genome is comprised mostly of junk — about 98-99%! Only 1 or 2 % of it codes for the building blocks of proteins. Scientists presumed that these noncoding regions are unnecessary and therefore viewed as an evolutionary mess in our genome. Apparently, half of our genome is comprised of jumping genes, and the most common is the long interspersed nuclear element-1 (LINE1).1

Jumping genes — parasitic stowaways

While some people view jumping genes as slackers that add up to the pile of junk littering our genome, others see them as parasitic stowaways. Because they can “jump” at seemingly random sites in the genome, they could insert themselves where they might cause gene disruptions, deleterious mutations, and chromosomal rearrangements resulting in diseases, including cancer.3

LINE1 — a paradoxical jumping gene

LINE1 (a jumping gene) is crucial during embryonic development

Researchers from the University of California – San Francisco recently reported that LINE1 (a jumping gene) is crucial during embryonic development. LINE1 accounts for 20% or more of the human genome. It is a retrotransposon, meaning it is amplified by first transcribing a segment of DNA into RNA, and then reverse-transcribed into DNA. The extra DNA copy will then be inserted at a different site in the genome.2 This jumping gene apparently acts as a critical regulator during the early embryonic development. It appears indispensable for an embryo to develop past the two-cell stage.1 This finding seems paradoxical since LINE1 has been implicated in various diseases, particularly cancers.4 Nevertheless, the important role of LINE1 was revealed when it was eliminated from the fertilized eggs, and consequently, they all remained at the two-cell phase. Accordingly, the role of the jumping gene in embryonic development is associated with the LINE1 RNA forming a complex with Nucleolin and Kap1 (gene regulatory proteins). The complex is believed to regulate embryonic development by turning off the dominant genes orchestrating the embryo’s two-cell state as well as by turning on the genes that promote further cell divisions and development.1

Jumping genes are mostly underappreciated largely because they are believed to be contributors to a pile of genetic junk or as parasitic stowaways. Despite being regarded as such, recent findings poised them as crucial genes. While most studies focus on the 1-2% of the genome performing a blatantly important role, i.e. to code for amino acids whereby a protein could be spectacularly built from, the recent study implicates that the jumping genes, too, deserve a spot in the research field.